The invention relates to a suction drill unit mounted in an at least partially rotary and percussive acting hand tool for the anchorage of a dowel in rock or rocklike material, such as concrete and masonry.
Drills for hand tools exhibit at one end an insertion end with rotary driver grooves and locking grooves for receiving the drill tool in the hand tool chuck.
For installing dowels, a drill dowel externally radially surrounding the drill and abutting at an axial stop collar is installed into the bore hole simultaneously when drilling a hole of greater diameter than that of the drill head and the drill bit is subsequently removed. A conventionally longitudinally slit, tubular drill dowel made of sheet metal is radially compressed when being installed and thus elastically radially stressed.
According to DE2548100 rock suction drills are disclosed for hand tools.
According to U.S. Pat. No. 4,635,738 a drill head formed of hard material is mounted on a bit shank and has an eccentrically arranged drill bit tip for boring a hole larger than the bit head diameter along with flushing liquid channels extending longitudinally to the bit head, whereby a drill wash channel passes through the bit head and radially and axially flushing liquid channels are formed.
EP0878261A1 discloses a helical drill bit for installing drill dowels that has an insertion end with rotary drive slots and locking slots, a tapered helical shank with a stop collar and a cutting edge with an eccentrically arranged pilot tip made of hard material for drilling a hole larger than the drill head diameter. The limited quantity of drilled material at the drill head is conveyed by a spiral grooved flute situated between the helical bit and the drill dowel and causes a limitation at higher bore output.
The primary object of the present invention is to provide an increase in the amount of cutting material conveyed during drill dowel installation or an increase in drilling performance. Another object relates to the increase of the service life of the drill bit and improved anchorage of the drill dowel.
Essentially, a suction drill unit is comprised of an insertion end for receipt into an at least partially rotary and percussive acting hand drilling tool device with a reduced diameter shank with a suction passageway running at least partially longitudinally along the shank and a radial connection opening secured thereto for the tight connection with a non-rotary suction head and an eccentrically arranged drill bit head for drilling of a hole larger than that of the drill bit head diameter, whereby the suction passageway opens adjacent the drill bit head.
In a tubular suction drill bit, compared to a helical drill bit with comparable pressure and torque resistance, at a given bore hole diameter there is a greater conveyance section available for removal of drilled material, whereby the quantity conveyed is further adjustable by the suction pressure and thus is independent of the speed. Due the structural enhancement of the tube compared to the helical shank, the increase in resistance and rigidity under variable flexure and due to the increase in fastening surface area between the drill bit head and the shank the service life of the drill is increased. On the other hand, at identical material stressing of the drill, thicker walled and thus radially more rigid dowels can be installed, since there is no requirement of available space for drilled material dust or cuttings. Furthermore, on removal there is no abraded, loose material pressed between the dowel and the walls of the bore hole, whereby the frictional-locking fit of the drill dowel in the bore hole is enhanced.
Advantageously, the suction passageway exits immediately behind the bit head transverse to the tool axis and out of the reduced diameter shank.
Because of the arrangement of the suction aperture immediately behind the bit head, the drilled material can be suctioned off between the bit head and the dowel into an axially extending space that is formed substantially inwardly of the bore hole walls and within the shank.
The bit head is advantageously comprised entirely of hard material or is inset with a hard material, whereby the penetration of the drilling head tip into the material to be excavated is improved and wear is reduced.
Further advantageously, the drilling head exhibits an advantageous single, recessed main cutting edge, whereby the eccentric bit tip, acting as a pilot cutting edge, assures effective guidance of the suction bit.